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CarbonЦCarbon Bond Formation at a Neutral Terminal Carbido Ligand Generation of Cyclopropenylidene and Vinylidene Complexes.

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Zuschriften
Carbido Complexes
DOI: 10.1002/ange.200601652
Carbon–Carbon Bond Formation at a Neutral
Terminal Carbido Ligand: Generation of
Cyclopropenylidene and Vinylidene Complexes**
Stephen R. Caskey, Michael H. Stewart,
Marc J. A. Johnson,* and Jeff W. Kampf
Olefin metathesis is an important tool for organic and
polymer synthesis.[1] However, some key functional groups
are not tolerated even by Ru-based catalysts.[2] We recently
showed that vinyl esters can deactivate [Ru(CHPh)(PCy3)2Cl2] (1)[3] by quantitative formation of [Ru(C)(PCy3)2Cl2] (2)[4, 5] A rare neutral terminal carbido complex,[4–7] 2 is surprisingly stable and has few reported
reactions.[5–7] However, protonation of 2 by strong acid
yields catalysts that rapidly initiate olefin metathesis.[7] Thus,
2 is both a precursor to and a decomposition product of olefin
metathesis catalysts. We see 2 as a potential source of a C1
fragment. Accordingly, we describe herein the first CC
bond-forming reaction of this unusual compound.
The terminal carbido ligand in 2 is a poor nucleophile, as
shown by its failure to react with MeI, MeCOCl, and
PhCH2Br. Although 2 does not react with a variety of alkenes
and alkynes (see the Supporting Information), it reacts
cleanly with MeO2CCCCO2Me (dimethyl acetylenedicarboxylate, DMAD) over 4 h in C6H6. A new blue-purple
complex, 3, is formed as the carbido signal for 2 (13C NMR:
d = 471.8 ppm) is replaced by a new signal at d = 195.7 ppm.
The 1H NMR spectrum evinces formation of a 1:1 adduct of 2
with DMAD. Formation of the cyclopropenylidene complex
[Ru{=CC2(CO2Me)2}(PCy3)2Cl2] (Scheme 1) accounts for
these observations. Several cyclopropenylidene complexes
exist. Unlike 3, however, the cyclopropenylidene units in
these complexes are substituted by phenyl or electrondonating
groups.[8–23]
[Ru(C)(H2IMes)(PCy3)Cl2]
(4;
H2IMes = 4,5-dihydro-1,3-bis(mesityl)imidazol-2-ylidene)
reacts similarly with DMAD, but the reaction is not clean
since the product reacts further with DMAD before all of 4
Scheme 1. Formation of 3 and ring-opening reactions. HBpin = pinacolborane, Ar = 3,5-Me2C6H3.
has been consumed. However, 4 reacts more cleanly with
HCCCO2Me (see the Supporting Information).
Single-crystal X-ray diffraction confirmed the structure of
3.[24] Figure 1 depicts a thermal ellipsoid plot of one of the two
chemically equivalent but crystallographically independent
molecules of 3 in the crystal. The data establish the expected
connectivity in 3, but the large uncertainty associated with the
Ru=C bond length of 1.846(10) A precludes comparison with
those in related alkylidene complexes. The cyclopropenylidene ring lies in the Cl-Ru-Cl plane. The structure shows
significant bond localization in the cyclopropenylidene fragment. These distances closely resemble those observed in free
[*] S. R. Caskey, M. H. Stewart, Prof. M. J. A. Johnson, Dr. J. W. Kampf
Department of Chemistry
University of Michigan
930 North University Avenue
Ann Arbor, MI 48109-1055 (USA)
Fax: (+ 1) 734-647-4865
E-mail: mjaj@umich.edu
[**] This report is based upon work supported by the National Science
Foundation under grant number CHE-0449459. We thank the
Research Corporation, the University of Michigan, and the Camille
and Henry Dreyfus Foundation for support. S.R.C. thanks the
University of Michigan Chemistry Department for Margaret and
Herman Sokol and Robert W. Parry Fellowships.
Supporting information for this article (including complete experimental details for new reactions) is available on the WWW under
http://www.angewandte.org or from the author.
7582
Figure 1. X-ray crystal structure of 3 (50 % thermal ellipsoids). Selected
bond lengths [.] and angles [8]: Ru1-C1 1.846(10), Ru1-Cl1 2.389(3),
Ru1-Cl2 2.402(3), Ru1-P1 2.407(3), Ru1-P2 2.390(3), C1-C2 1.410(13),
C1-C3 1.425(14), C2-C3 1.300(14); C1-Ru1-Cl1 91.6(3); C1-Ru1-Cl2,
95.3(3), C1-Ru1-P1 97.0(3), C1-Ru1-P2 95.8(3), C2-C1-C3 54.6(7), C1C2-C3 63.3(7), C1-C3-C2 62.1(7).
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. 2006, 118, 7582 –7584
Angewandte
Chemie
C3(NiPr2)2 (5)[25] and in other cyclopropenylidene complexes.[9, 14–23]
The formation of 3 from 2 is interesting because the
cyclopropylidene
complex
[Ru{=CC2H2(CO2Me)2}(PCy3)2Cl2] (6) is not observed as an intermediate when 2 is
formed from 1 by reaction with FeistBs ester.[4] Addition of
2 equivalents or less of PCy3 to [Ru{=CC2H2(CO2Me)2}(PPh3)2Cl2] similarly yields 2. In this case, too, 6 is not seen.[6]
The 13C NMR shifts of the ring atoms in 3, 195.7 and
162.2 ppm, closely resemble those observed for 5[25] but less so
other cyclopropenylidene complexes, for which some cyclopropenium character is often invoked.[14–23] Unlike 1, 3 does
not react appreciably with common olefins or alkynes,
although under some conditions small amounts of 2 are
formed, suggesting reversibility of the 2!3 transformation
(see the Supporting Information). However, several reagents
effect 1,1-addition of HX to the ring to form vinylidene
complexes 7–10; reaction with pyridine-N-oxide similarly
yields 11 (Scheme 1). Cyclopropenium character could
account for the observed reactivity, as all the reagents
shown can act first as nucleophiles; however, there may be
other explanations.
The structure of one vinylidene complex, [Ru{=C=C(CO2Me)CH(NHAr)CO2Me}(PCy3)2Cl2]
(7,
Ar = 3,5Me2C6H3), was determined by single-crystal X-ray diffraction.[26] The vinylidene unit is apical in square-pyramidal 7
(Figure 2).
Figure 2. X-ray crystal structure of 7 (50 % thermal ellipsoids). Selected
bond lengths [.] and angles [8]: Ru1-C37 1.7458(17), Ru1-Cl1
2.3441(4), Ru1-Cl2 2.3454(4), Ru1-P1 2.4405(4), Ru1-P2 2.4098(4),
C37-C38 1.344(2); C37-Ru1-Cl1 105.16(5), C37-Ru1-Cl2 100.68(5), C37Ru1-P1 95.78(5), C37-Ru1-P2 93.39(5), Ru1-C37-C38 176.16(14), C37C38-C39 118.76(16), C37-C38-C41 121.94(16), C39-C38-C41
119.23(15).
Ruthenium vinylidenes are useful as catalysts and catalyst
precursors for olefin metathesis, alkyne dimerization, and
other reactions.[27, 28] Like the “parent” vinylidene complex
[Ru(=C=CH2)(PCy3)2Cl2],[3] 7–11 do not catalyze the ringclosing metathesis of diethyl diallylmalonate, but they do
polymerize norbornene.
In summary, terminal carbido complex 2 undergoes
[2+1] addition with DMAD to yield the cyclopropenylidene
complex 3. Complex 4 reacts similarly with HC=CCO2Me in
Angew. Chem. 2006, 118, 7582 –7584
the first CC bond-forming reactions reported for neutral
terminal carbido complexes. Protic reagents HX (X = OH,
OPh, NH(3,5-Me2)C6H3) as well as pinacolborane add in a 1,1
manner to one of the distal ring C atoms in 3, forming
vinylidene complexes 7–11 in high yield. We are currently
exploring the reactivity of 7–11 as well as seeking a means of
regenerating a metathesis-active alkylidene complex or the
carbide complexes 2 and 4.
Received: April 26, 2006
Revised: July 19, 2006
Published online: October 17, 2006
.
Keywords: carbides · cycloaddition ·
cyclopropenylidene ligands · ruthenium · vinylidene ligands
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[24] Crystal data for 3·1.5 CH2Cl2 : C44.50H75Cl5O4P2Ru, monoclinic,
P21/c, a = 11.926(2), b = 18.555(3), c = 45.638(8) A, b =
96.800(3)8, V = 10 028(3) A3, Z = 8, 1calcd = 1.344 g cm3, MoKa
radiation, l = 0.71073 A, T = 123(2) K, 43 778 measured reflec-
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.de
7583
Zuschriften
[25]
[26]
[27]
[28]
7584
tions, 8524 unique (Rint = 0.1875), 4942 reflections with Inet >
2.0(Inet), m = 0.681 mm1, min/max transmission = 0.8758 and
0.9412, R1 (I > 2s) = 0.0775, wR2 = 0.1954, GoF = 1.066, no. of
parameters = 1056, final difference map within 1.008 and
1.258 e A3. CCDC-604841 (3·1.5 CH2Cl2) contains the supplementary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
V. Lavallo, Y. Canac, B. Donnadieu, W. W. Schoeller, G.
Bertrand, Science 2006, 312, 722.
Crystal data for 7: C51H83Cl2NO4P2Ru, monoclinic, P21/c, a =
15.5355(8), b = 18.9133(10), c = 17.5169(9) A, b = 97.403(1)8,
V = 5104.0(5) A3, Z = 4, 1calcd = 1.312 g cm3, MoKa radiation,
l = 0.71073 A, T = 123(2) K, 101 108 measured reflections,
12 702 unique (Rint = 0.0321), 11 419 reflections with Inet > 2.0(Inet), m = 0.518 mm1, min/max transmission = 0.8197 and
0.8602, R1 (I > 2s) = 0.0295, wR2 = 0.0740, GoF = 1.059, no. of
parameters = 554, final difference map within 0.885 and
0.727 e A3. CCDC-604842 (7) contains the supplementary
crystallographic data for this paper. Data can be obtained as in
Reference [24].
C. Bruneau, P. H. Dixneuf, Angew. Chem. 2006, 118, 2232;
Angew. Chem. Int. Ed. 2006, 45, 2176.
H. Katayama, F. Ozawa, Coord. Chem. Rev. 2004, 248, 1703.
www.angewandte.de
2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. 2006, 118, 7582 –7584
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bond, neutral, vinylidene, carbonцcarbon, cyclopropenylidene, generation, formation, terminal, complexes, ligand, carbide
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